A turbocharger may be provided in an engine to increase engine torque or power output density. The turbocharger may include an exhaust-driven turbine coupled to a compressor via a drive shaft. The compressor may be fluidly coupled to an air intake manifold in the engine that delivers air to a plurality of engine cylinders. Exhaust flow from one or more engine cylinders may be directed to a turbine wheel, causing the turbine to rotate about a fixed axis. The rotational motion of the turbine drives an impeller (e.g., wheel) of the compressor, which compresses air into the air intake manifold to increase boost pressure during select engine operating conditions.
Compressor efficiency influences overall engine performance and fuel consumption. For example, lower compressor efficiency may result in slow engine transient response and higher fuel consumption for both steady-state and transient engine operation. At lighter engine loads, when compressor efficiency is reduced, there may be increased turbocharger lag during a tip-in. Additionally, compressor surge limits may restrict boost pressure rise at low engine speeds.
Compressors are prone to surge during events that lead to an increased pressure ratio across the compressor or decreased mass flow into the compressor. For example, when an operator rapidly tips-out an accelerator pedal, air flow into the compressor inlet decreases, reducing the forward flow through the compressor while the compressor is still at a high pressure ratio. This may lead to pressure accumulation at an outlet end of the compressor, driving air in a reverse direction that may degrade components of the compressor. Thus, extending a margin to surge may increase a range of conditions through which compressor operation remains stable.
Turbocharger compressors may be adapted with a mechanism to relieve pressure at the compressor outlet, in particular for turbochargers coupled to diesel engines. Larger turbochargers may be used to provide high boost pressures for diesel engine operation. However, the benefits of high boost pressure supplied by the turbocharger compressor may be offset by a higher likelihood of compressor surge. Thus, turbocharger compressors for diesel engine applications may be configured to reduce a likelihood of surge occurring by providing a path for flow recirculation. For example, the compressor may include a bleed valve that vents intake pressure to atmosphere or, alternatively, the compressor may comprise a ported shroud. The ported shroud may be a passage within an inner casing of the compressor inlet that allows air to flow in a reverse direction through the compressor, returning compressed air from the compressor outlet to the compressor inlet to lower the pressure ratio and increase mass flow into the compressor. While the ported shroud effectively reduces a likelihood of compressor surge, the presence of the ported shroud may also adversely affect compressor efficiency, especially at low compressor speeds.
Various approaches have been developed to address the issue of compressor efficiency at low mass flow rate, including combining a mechanism for reducing compressor outlet pressure with a device for controlling flow into the compressor inlet. One example approach is shown by Pekari et al. in U.S. Pat. No. 4,403,912. Therein, an engine compressor with an air bleed valve and variable guide vanes is disclosed. The bleed valve is opened to vent pressure in the compressor to maintain stable compressor operation, the opening and closing of the valve adjusted by an actuator that also controls a position of the variable guide vanes. The variable guide vanes are at a specified attitude during initial engine operation with the bleed valve fully open. The actuator adjusts the bleed valve as the engine accelerates until the bleed valve is in a fully closed position, after which continued actuation actuates the guide vanes to an attitude to enable maximum compressor operation.
However, the inventors herein have recognized potential issues with such systems. As one example, the positioning of the guide vanes relative to the compressor inlet in the system of U.S. Pat. No. 4,403,912 may not control a flow area of the inlet sufficiently to elicit a rapid and effective response to changes in compressor stability. Furthermore, the actuation of the guide vanes only after the bleed valve is fully closed may limit flow control through the compressor and result in reduced compressor efficiency.
In one example, the issues described above may be addressed by a system for a compressor, comprising: a casing forming a recirculation passage surrounding an inlet conduit; an active casing treatment surrounding the inlet conduit and configured to selectively control gas flow through the recirculation passage; an impeller; a volute; and an adjustable device positioned in the inlet conduit upstream of the impeller, at least partially overlapping with a plane of the volute, configured to selectively reduce an effective size of the impeller. In this way, by including the adjustable device at a position that selectively reduces an effective size of the impeller, a flow range of the compressor may be increased at lower compressor pressure ratios and mass flows while compressor efficiency is increased. Furthermore, by selectively enabling the gas flow through the recirculation passage, the flow range of the compressor may be increased at higher compressor pressure ratios and mass flows while avoiding compressor efficiency penalties at lower compressor pressure ratios and mass flows.
As one example, a bleed port may fluidically couple the inlet conduit to the recirculation passage downstream of a leading edge of the impeller, and a recirculation port may fluidically couple the inlet conduit to the recirculation passage upstream of the adjustable device. A valve positioned at one of the bleed port and the recirculation port may enable the recirculation passage to be selectively blocked. For example, adjusting the valve to a closed position may block the gas flow through the recirculation passage while adjusting the valve to an open position may enable gas flow through the recirculation passage. As another example, the adjustable device may include a plurality of adjacently arranged vanes forming a ring about a central axis of the compressor, an actuation plate coupled to an actuator, and a plurality of handles connecting the plurality of vanes to the actuation plate. Interior edges of the vanes of the adjustable device may form a flow passage through the adjustable device that is aligned along the central axis, each of the vanes being rotatable about an actuation axis arranged radially to the central axis. The vanes may be rotatable between an open position having a larger radius flow passage and a closed position having a smaller radius flow passage via the actuator, the actuation plate, and the handles. In this way, the adjustable device and the valve may be independently adjusted to rapidly vary the effective size of the impeller and gas flow through the recirculation passage, respectively, resulting in a wide compressor flow range and high compressor efficiency.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.